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A large number of gases are releasing from the medium-high temperature geothermal fields distributed along the large-scale strike-slip fault zones in the southeastern margin of the Tibetan Plateau. In this study, 11 hot spring water and the associated bubbling gas samples were collected along the Xianshuihe-Anninghe fault zones (XSH-ANHFZ) and analyzed for chemical and isotopic compositions. The $${\delta ^{18}}{{\rm{O}}_{{{\rm{H}}_2}{\rm{O}}}}$$ and $$\delta {{\rm{D}}_{{{\rm{H}}_2}{\rm{O}}}}$$ values indicate that hot spring waters are predominantly meteoric origin recharged from different altitudes. Most water samples are significantly enriched in Na+ and HCO3− due to the dissolution of regional evaporites, carbonates and Na-silicates. 3He/4He ratios of the gas samples are 0.025–2.73 times the atmospheric value. The 3He/4He ratios are high in the Kangding region where the dense faults are distributed, and gradually decrease with increasing distance from Kangding towards both sides along the Xianshuihe fault zones (XSHFZ). Hydrothermal fluids have dissolved inorganic carbon (DIC) concentrations from 2 to 42 mmol L−1, δ13CDIC from −6.9‰ to 1.3‰, $${\delta ^{13}}{{\rm{C}}_{{\rm{C}}{{\rm{O}}_2}}}$$ from −7.2‰ to −3.6‰ and Δ14C from −997‰ to −909‰. Combining regional geochemical and geological information, the CO2 sources can be attributed to deep-sourced CO2 from mantle and metamorphism of marine carbonate, and shallow-sourced CO2 from the dissolution of marine carbonate and biogenic CO2. The mass balance model shows that 11±6% of the DIC is sourced from the dissolution of shallow carbonate minerals, 9±8% formed by pyrolysis of sedimentary organic matter, 80±9% derived from deep metamorphic origin and mantle-derived CO2. Among them, the deep-sourced CO2 in Anninghe fault zones (ANHFZ) is merely metamorphic carbon, whereas ca. 12% and ca. 88% of the deep-sourced CO2 in the XSHFZ are derived from the mantle and metamorphic carbon, respectively. The average deep-sourced CO2 flux in the Kangding geothermal field is estimated to be 160 t a−1. If all the hot springs in various fault zones in the southeastern margin of the Tibetan Plateau are taken into account, the regional deep-sourced CO2 flux would reach ca. 105 t a−1. These results show that the deep-sourced CO2 released from non-volcanic areas might account for a considerable proportion of the total amount of global deep-sourced carbon degassing, which should be paid more attention to.

Thermal manifestations are commonly found in central Mexico as result of the volcanic activity originating from the formation of the Trans-Mexican Volcanic Belt during the Quaternary. The Rancho Nuevo hot spring is one of them that has not been described before with a discharge temperature near 92 °C. The goal of the present study is to provide geothermal characteristics of thermal manifestations at Rancho Nuevo location based on geochemical and mineralogical results to explain deep-subsurface processes that occurred in the geothermal system. The presence of kaolinite, montmorillonite, opal, zeolite, barite, pyrite, and stibnite in altered soil sediments or around the hot springs identified by the techniques used in the present study, confirms the presence of hydrothermal activity. In addition, based on the X-ray diffraction, calcite precipitates at the surface of the thermal springs. This mineral association reflects deep geothermal processes and is eventually deposited in shallow zones. Fluid mixing processes and variations in redox conditions are suggested by mineral association and isotopic sulfur data. Finally, based on the physicochemical data provided by the water samples and the discharge conditions of the springs, stability diagrams were constructed for pyrite, barite, and zeolites using the Geochemist’s Work Bench program to corroborate these data with the mineralogical results. The mineralogical results and distribution, as well as the N-S trend of mineral associations suggest interaction processes between geothermal fluid and rocks of the stratigraphic sequence, and active major faults, enabling the upward flow of deep geothermal fluids. The approach to the conceptual model of the Rancho Nuevo geothermal prospect reveals an attractive potential for the exploration of a viable geothermal resource in central Mexico.

Many of therapeutic treatments in spas are concentrated on mud therapy. Clays are included in the formulation of thermal mud as vehicles of the mineral medicinal water. To be suitable for therapeutic use, some mineralogical, rheological and thermal properties should be respected in order to be topically applied. Our objective is to explore the suitability of three Tunisian commercial green clays traditionally used as facial and body masks by women in the region of Douiret (CD), Tozeur (CT) and Korbous (CK) in terms of their physicochemical structure chemical composition, heavy metals risk assessment, thermal properties, plasticity, rheology and their potential application as peloid with distilled and sodium chloride-rich sulfated thermal waters from hot spring in the region of hammam Lif and Korbous and sea waters. The mineralogy of samples (clay fraction and associated minerals) was determined by X-ray powder diffraction and FT-IR analysis, and the chemical composition was obtained by ICP. The main clay fraction of the samples was smectite and illite with significant amount of kaolinite. Regarding their mineralogical properties, the samples with a high amount of smectite fraction are more suitable for use in Tunisian spas and for the application as peloids. The thermal analyses of clay powders shows a specific heat value comparable to those use used in spas. Also the muds showed a low cooling rate which is necessary for therapeutic use. Rheological properties of peloids prove their thixotropic characteristics.

Fungi are considered to be the most resilient and economically important microbial community that can easily survive and optimally grow under a wide range of growth conditions. Thermophilic fungi from the geothermal sources have been less pondered upon and lie unexplored. Here, a microbiome approach was conducted to understand the concealed world of the environmental mycobiota from the two hot springs of North Sikkim district located in North-east India. The solfataric muds from the hot springs were analyzed. In both the samples, on the basis of genus level classification, genus Fusarium had the highest abundance followed by Colletotrichum, Pochonia, Pyricularia, Neurospora, etc. Analyzing the predicted genes, the functional proteins of New Yume Samdung mycobiome were found to be dominated by the genera Fusarium (22%), Trichoderma (12%), and Aspergillus (11%), whereas in the case of Old Yume Samdung, it was dominated by the genera Aspergillus (11%), Saccharomyces (6%), and Fusarium (5%). Interestingly, in the studied mycobiome, environmental yeasts were also detected. From the functional metagenomics, sulfate adenylatetransferase (SAT) proteins for sulfur assimilation were found in some of the fungal reads. Toxin protein reads such as AM-toxin biosynthesis proteins, AF-toxin biosynthesis proteins, Gliotoxin biosynthesis proteins, and aflatoxin biosynthesis proteins were detected in the mycobiomes.

Fluoride contamination in groundwater is a major problem throughout the world as well as in India. High-fluoride content was reported in the hot springs of Atri and Tarbalo sites in Odisha, India, and residents of nearby villages showed the manifestations of fluorosis. Around 39% of the groundwater samples showed fluoride concentration > 1 mg/l, higher than the desirable limit specified by the WHO. The dominant chemical facies of groundwaters were ions of Ca-Mg-HCO3 and Ca-Na-Cl, which infers the lithological control over the hydrochemistry of this area. A strong correlation between fluoride and other major ions could not be found, suggesting that multiple processes are responsible for the enriched fluoride concentration observed in the study area. The major geochemical processes include dissolution of fluoride-bearing minerals from the rocks, evapotranspiration, agricultural input and mixing of cold groundwater with hot spring water containing high fluoride. The maximum fluoride exposure doses through drinking water from fluoride-contaminated tube wells were estimated to be 0.07 mg/kg/d for infants, 0.125 mg/kg/d for children and 0.06 mg/kg/d for adults, which are higher than the minimum risk level (0.05 mg/kg/d). Exposure doses of fluoride indicate that exposure risk is doubled for children in comparison to infants and adults, which might cause severe dental fluorosis and other ailments. Considering the environmental and hydrological set up of the study area, membrane defluoridation process can be suggested as the best remediation method. Nalgonda technique, dilution of fluoride-rich groundwater and better nutrition containing calcium and vitamin C are other possible options that can be included for early mitigation of fluoride contamination.

Dangxiong Co is a salt lake located in the center of the Tibetan Plateau, China. We studied the petrology, mineralogy, geochemistry and microfossil assemblages in the Quaternary, first terrace of Dangxiong Co. Limnocytherellina was the most common ostracode in the first terrace and prefers warm-humid conditions. Grainy ankerite in the terrace exhibits obvious overgrowth edges and uneven surfaces. Rare earth elements and Y distribution patterns in the first terrace show moderate rare earth enrichment, whereas Eu and Dy show weak negative and positive anomalies, respectively. These features indicate that the first terrace in Dangxiong Co is composed of lacustrine hydrothermal deposits. Moreover, the δ11B value of the Quaternary travertine is low, reflecting the low values in hydrothermal waters of the Quaternary. We suggest that hydrothermal water has been an important source of boron in the Quaternary. The three rivers on the south side of Dangxiong Co contribute 95% of the B2O3. The geochemical characteristics and the δ11B values of the waters in these three rivers are the same as in waters from Maerzuo hot spring. Thus, the hot spring is still the main source of boron to Dangxiong Co. These results have important implications for future exploration of borate deposits in salt lakes.

The Jimo hot spring in Shandong Peninsula, China, is a typical coastal geothermal system. The geothermal water has a very high salinity (10.8 g/L) and the origin of the salt is key to utilization of this geothermal resource. A systematic investigation of the hydrochemistry and isotopes (δ11B, 87Sr/86Sr, δ18O, δD, 13CDIC and 14CDIC) of water from 14 geothermal wells was conducted. The results show that the geothermal waters from the high-temperature center and eastern part of the geothermal field are Cl-Na·Ca-type waters with Br/Cl (8 × 10−4–1.0 × 10−3), Na/Cl (0.63–0.70) and δ11B values (15.9–17.2‰) that are lower than those of seawater. The western geothermal waters are dominated by Cl-Na-type waters with Br/Cl and Na/Cl values similar to those of seawater. The depleted δD and δ18O compositions and the corrected 14CDIC age suggest that Jimo geothermal waters are mixtures of late Pleistocene to early Holocene and younger meteoric waters. An improved Br/Cl-Na/Cl diagram, ion mass balance calculations and δ11B values indicate that halite and K-salt dissolution and subsequent cation exchange formed the dominant Cl-Na·Ca-type geothermal water, and this was then modified into a small amount of Cl-Na-type water in the western area by mixing with minor seawater entrapped in the unconsolidated sediments. The 87Sr/86Sr ratios (0.710613–0.710726) of the geothermal waters reflect water–rock reactions in the sandstone. The improved Br/Cl-Na/Cl diagram, Piper plot and boron isotopic dataset containing saline waters from coastal geothermal systems worldwide further confirm that the salinity in the Jimo geothermal water originated from dissolution of marine evaporites.

Hot springs are fascinating extreme environments for the isolation of polyextremophilic microorganisms with extraordinary characteristics. Since polyextremophilic bacterial growth are not as high as routine bacteria, the objective of this study was to investigate the effect of some environmental factors on biomass and metabolites productions in the newly isolated strain, from Larijan hot spring in Iran. The strain was identified as Aeribacillus pallidus Lhs-10 and deposited as CCUG 72355 and IBRC-M 11202 in Sweden and Iran, respectively. This thermoalkaliphilic strain can grow best at 50 °C, pH 8 and in the presence of 25 g/l NaCl. The physiological characterization of this strain show that [Ca/Mg] ratio affect its growth and biomass production with the best results obtained at the ratio of 2.5. Moreover, lactic and acetic acids production by this strain was affected by pH, aeration, and temperature, where a metabolic shift was detected from lactate to acetate production when the culture was aerated. Besides, its spores could tolerate heating at 80, 85, 90, 95 and 98 °C for 30 min without any reduction in the initial spore population, whereas D-value was defined 50 min at 98 °C. This newly lactic acid-producing strain of A. pallidus can be a promising strain that can be used in the harsh conditions in industrial processes.

The Mangka saline hot springs, in the Simao Basin in southwest China, are unique in having relatively large discharge (>10 L/s) from the red beds (relatively poor permeability) and travertine deposition from Cl-Na type hot water with high content of total dissolved solids (10 g/L). The stable hydrogen and oxygen isotopes indicate that the Mangka spring waters are meteoric in origin and the average altitude of the recharge area is estimated as 1,750 m above sea level. The high temperature of the spring water is derived from geothermal heating. The estimated geothermal reservoir temperature range is 86–91 °C and the circulation depths of the spring waters are 2,318–2,454 m. Incongruent dissolution of salt-bearing formations contributes to the mineralization of the Mangka saline hot springs, including dissolution of halite, gypsum, carbonate and sylvite. Some suitable hydrochemical factors provide beneficial conditions for travertine deposition such as a higher CO2 partial pressure of 10–1.94–10–0.9, γCa/γHCO3 (the milliequivalent ratio of Ca and HCO3) ranging from 5.76 to 6.67, and saturation indices for both calcite and aragonite over or equal to zero. There is also a favorable hydrodynamic condition for the spring water flowing down steep slopes and forming fast-flowing shallow channels with a relatively large surface area. The formation of the Mangka saline hot springs is summarized as follows: the groundwater receives recharge of infiltration from precipitation, undergoes deep circulation in the salt-bearing strata, receives heat from the geothermal heat flow, and ascends to the land surface along the permeable fault.

Temperature and bioavailable energy control the distribution of life on Earth, and interact with each other due to the dependency of biological energy requirements on temperature. Here we analyze how temperature-energy interactions structure sediment microbial communities in two hydrothermally active areas of Guaymas Basin. Sites from one area experience advective input of thermogenically produced electron donors by seepage from deeper layers, whereas sites from the other area are diffusion-dominated and electron donor-depleted. In both locations, Archaea dominate at temperatures >45 °C and Bacteria at temperatures, Lagostina et al. show that relative abundances of Bacteria and Archaea in sediments of Guaymas Basin, Gulf of California, are controlled by temperature, while energy flux explains microbial community structure at the phylum-level and below. Hot diffusion-dominated and energy-depleted sediments are dominated by taxa with relatives in cold subseafloor sediments, while hot sediments with high energy supply from fluid seepage are dominated by taxa also found at hydrothermal vents and in hot springs.

Satellite thermal infrared remote sensing is an important technique for exploring and monitoring thermal properties of hot spring regions. We used Landsat 8 Optical Land Imager (OLI)–Thermal Infrared Scanner (TIR) sensor images to observe the thermal status of three hot spring areas in the United Arab Emirates for the first time in 2017. Landsat 8 TIR band 10 images were used to estimate land surface temperatures (LST) using a mono-window algorithm, emissivity using a normalized difference vegetation index (NDVI) threshold method, and radiative heat fluxes (RHF) and heat discharge rates (HDR) using the Stefan–Boltzmann law and a relationship coefficient. The highest maximum LST were about 43°C, 40°C, and 27°C at the Ain Al Faidha (AF), Green Mubazzarah (GM), and the Ain Khatt (AK) hot spring areas, respectively. The LST were about 13°C, 10°C, and 4°C above the pixel (30 m × 30 m) average ambient temperatures, although point LSTs might be higher than these. The highest RHF were 68, 83, and 21 W/m2, and total radiative heat losses approximately 157, 530, and 15 MW, at GM, AF, and AK, respectively. Total HDR were estimated to be 1013, 3423, and 94 MW for GM, AF, and AK, respectively, using a relationship coefficient between HDR and RHF of 6.49. The LST and RHF increased with decreasing NDVI value, i.e., bare or desert surface showed higher values than vegetated surface. This study indicates that satellite remote sensing is a cost-effective and efficient method for assessing the thermal components of hot springs.

Background Terrestrial hot spring settings span a broad spectrum of physicochemistries. Physicochemical parameters, such as pH and temperature, are key factors influencing differences in microbial composition across diverse geothermal areas. Nonetheless, analysis of hot spring pools from the Taupo Volcanic Zone (TVZ), New Zealand, revealed that some members of the bacterial genus, Acidithiobacillus, are prevalent across wide ranges of hot spring pHs and temperatures. To determine the genomic attributes of Acidithiobacillus that inhabit such diverse conditions, we assembled the genomes of 19 uncultivated hot spring Acidithiobacillus strains from six geothermal areas and compared these to 37 publicly available Acidithiobacillus genomes from various habitats. Results Analysis of 16S rRNA gene amplicons from 138 samples revealed that Acidithiobacillus comprised on average 11.4 ± 16.8% of hot spring prokaryotic communities, with three Acidithiobacillus amplicon sequence variants (ASVs) (TVZ_G1, TVZ_G2, TVZ_G3) accounting for > 90% of Acidithiobacillus in terms of relative abundance, and occurring in 126 out of 138 samples across wide ranges of temperature (17.5–92.9 °C) and pH (1.0–7.5). We recovered 19 environmental genomes belonging to each of these three ASVs, as well as a fourth related group (TVZ_G4). Based on genome average nucleotide identities, the four groups (TVZ_G1-TVZ_G4) constitute distinct species (ANI Acidithiobacillus species (TVZ_G2-TVZ_G4) and one belongs to Acidithiobacillus caldus (TVZ_G1). All four TVZ Acidithiobacillus groups were found in hot springs with temperatures above the previously known limit for the genus (up to 40 °C higher), likely due to significantly higher proline and GC contents than other Acidithiobacillus species, which are known to increase thermostability. Results also indicate hot spring-associated Acidithiobacillus have undergone genome streamlining, likely due to thermal adaptation. Moreover, our data suggest that Acidithiobacillus prevalence across varied hot spring pHs is supported by distinct strategies, whereby TVZ_G2-TVZ_G4 regulate pH homeostasis mostly through Na+/H+ antiporters and proton-efflux ATPases, whereas TVZ_G1 mainly relies on amino acid decarboxylases. Conclusions This study provides insights into the distribution of Acidithiobacillus species across diverse hot spring physichochemistries and determines genomic features and adaptations that potentially enable Acidithiobacillus species to colonize a broad range of temperatures and pHs in geothermal environments.

Safa Dam Tunnel to Golzar makes it possible to transfer water from Dam Safa to Kerman City. The tunnel, which is approximately 40 km long, is located in the Kerman Cenozoic magmatic arc as a part of the Dehaj-Sarduiyeh belt. The aim of this study was to investigate and identify the source of water resources around the tunnel path as well as the source of water entering the northern and southern parts of the tunnel. In this study, isotopes of oxygen, hydrogen (deuterium and tritium), and sulfur have been used. The values of these isotopes are first interpreted analytically on the reference graphs displayed in the next step. As a whole, 13 samples were taken for isotopic analysis from different parts of water resources around the tunnel path. In all samples, $$ {}{}^{18}O $$ and $$ {}{}^2H $$ were measured, and in addition, in 5 samples of $$ {}{}^{34}S $$ isotope and in seven samples $$ {}{}^3H $$ isotope values were measured as well. According to the isotopic composition, age of the samples, and hydrogeological conditions of the region, four types of water sources have been identified, which include the following: (1) meteoric waters (water samples of Chari and Dizin Mah Rivers, Mubarak Shah salt spring, Sarzeh and Ashkan, BH5 and artesian Shirink well), (2) hydrothermal waters (sample of Shirink hot spring water), (3) ancient waters (sample of water in the northern part of the tunnel), (4) ancient waters of snowmelt origin (southern part of the tunnel and BH4). The BH9 water sample is the result of mixing ancient water with ancient water from the source of snowmelt. Sulfur originates from water samples in the northern part of the tunnel and in the southern part of Thenardite sulfate (Na2SO4) mineral. In the source of sulfur, the samples of Shirink hot spring water and BH9, in addition to the extraction of Thenardite, also have some oxidation and reduction processes. The source of water sulfur of Ashkan spring was mainly fossil fuels and air currents. The results stated that the age of water samples shows a direct relationship with their depth.

High-temperature SiO2-rich springs are one of the most indicative manifestations of deep geothermal activities. Although they often represent the valuable geothermal potentials and significances of the areas, their high SiO2 contents usually bring some non-negligible problems when we exploit the geothermal resources, especially the silica scales. To understand the sedimentation sequences of SiO2-rich hot springs and to expose its potential relationships with natural sinter deposits and silica scales in geothermal plants, this study make a couple of analyses of the water and solid samples collected from a natural SiO2-rich hot spring in Tengchong (i.e. Dagunguo spring) and isothermal evaporation experiments, including water chemistry analyses, X-ray diffraction, thin-section observation, and electron microscopy analyses. The modern sinters in Dagunguo spring are amorphous SiO2 which is largely formed of tight siliceous layers and some amorphous SiO2 spheres. Some silicified microorganisms, elemental sulfur, and clay are also found. The Dagunguo spring water is Na–Cl–HCO3-type SiO2-rich water, with a pH of about 8 and low dissolved concentrations of Al3+, Fe3+ and Mg2+. Isothermal evaporation (T = 84 °C) resulted in a sequence of precipitated minerals: amorphous SiO2 → halite → sodium sesquicarbonate dihydrate (trona) → potassium chloride (sylvine), accompanied by calcite, hydrous sodium sulfate (mirabilite) and sodium bicarbonate (baking soda). The amorphous SiO2 produced in the evaporation experiments exhibited different shapes and structures than the spherical opal-A formed by hot spring water precipitation under natural conditions. The study of precipitation sequence and minerals of hot spring water provides insight into the scaling mechanism of silica-rich geothermal water and anti-scaling measures that can be applied in the process of exploitation and utilization of geothermal resources.

The true-branching cyanobacterium Fischerella thermalis (also known as Mastigocladus laminosus) is widely distributed in hot springs around the world. Morphologically, it has been described as early as 1837. However, its taxonomic placement remains controversial. F. thermalis belongs to the same genus as mesophilic Fischerella species but forms a monophyletic clade of thermophilic Fischerella strains and sequences from hot springs. Their recent divergence from freshwater or soil true-branching species and the ongoing process of specialization inside the thermal gradient make them an interesting evolutionary model to study. F. thermalis is one of the most complex prokaryotes. It forms a cellular network in which the main trichome and branches exchange metabolites and regulators via septal junctions. This species can adapt to a variety of environmental conditions, with its photosynthetic apparatus remaining active in a temperature range from 15 to 58 °C. Together with its nitrogen-fixing ability, this allows it to dominate in hot spring microbial mats and contribute significantly to the de novo carbon and nitrogen input. Here, we review the current knowledge on the taxonomy and distribution of F. thermalis, its morphological complexity, and its physiological adaptations to an extreme environment.

This study presents resistivity and geomagnetic surveys to identify the subsurface structure of Tatta Pani geothermal spring, Kotli, Jammu & Kashmir, Pakistan. The flow, extension and subsurface structures were investigated using 1D resistivity survey by applying the technique of Vertical Electrical Sounding using Schlumberger electrode configuration. The data were then fed into iterative software to obtain the resistivity of each layer and corresponding lithology. The resistivity structure of the spring revealed four distinct lithology units based on the resistivity contrast. The high resistivity unit (> 300 Ω-m) represented weathered dolomite/limestone of Abbottabad Formation. The low to moderate resistivity unit (80–200 Ω-m) comprised clay and sandstone layers of Patala Formation, having a potential of surface meteoric water. The low resistivity unit (20–80 Ω-m) interpreted as shaley to clay lithology was related to moderately altered hydro-thermally rocks. The low resistivity unit (5–20 Ω-m) demarcate the geothermal spring having high dissolved minerals. The thermal spring was concentrated on the right bank of River Poonch at a depth of 30 m below the surface and increased its depth in the North-East direction. The magnetic survey was performed to portray the deep-seated tectonics, magnetic signature of the rock and depth of the hot spring and was in agreement with the resistivity data. The magnetic intensity and anomaly changes were abrupt and smooth with the intensity variation of 460 nT, while the anomaly of – 75 nT to 60 nT representing a fault in the sedimentary sequence. The magnetic data showed two contrasting promising magnetic signatures of Patala Formation and anticlinal Abbottabad Formation, in line with the geology and resistivity data. The results showed that the resistivity structure of Tatta Pani geothermal spring is concentrated at the contact of a low resistivity rock of Patala Formation above and weathered and altered high resistivity underlying rocks of the Abbottabad Formation.

Hot spring dwelling cyanobacterial strain TA-9 was isolated and characterized using a polyphasic approach. Morphological evaluation of the strain indicated the presence of typical T-type true branching with differently positioned heterocytes. Physiological characterization of the strain was also performed followed by molecular and phylogenetic analyses based on 16S rRNA gene. 16S rRNA gene phylogeny indicated the strain to be strongly supported at an independent node with consistent tree topology being visible. Further, folding of the D1−D1′ and box-B helix of the ITS region differentiated the strain from phylogenetically related species. Thus, the morphological, phylogenetic and folded ITS structures confirm that the strain TA-9 is a new species of the genus Mastigocladus with the name proposed being Mastigocladus ambikapurensis in accordance with the International Code of Nomenclature of algae, fungi and plants.

The Zhacang thermal field has the highest temperature and the most typical characteristics among the 84 geothermal anomalies discovered in Qinghai Province, China. It is located 15 km southwest of Guide County and has a total area of 8.4 km2, where two geothermal wells have been drilled since 2011. This paper summarises the geological conditions, drilling data, geophysical exploration data, and hydrochemical characteristics of the Guide–Zhacang geothermal field. The Zhacang geothermal field has a high geothermal flow value and is rich in geothermal resources with high thermal conductivity (2.910 W/(m•K)) and high geothermal flow value (87–117 mW/m2). The main strata are made up of Neogene mudstone, Triassic sand slate, and Indosinian granite and granodiorite, which provide a good thermally insulating cover layer and storage zone. The Zhacang and Reguang faults are deep, which helps the deep heat source and underground hot water move upward. The source of borehole hot water and hot spring water in the Zhacang geothermal field is atmospheric precipitation with a recharge elevation of 3320–3470 m, and the circulation depth is −2888.6 m. The results of explorations and surveys are integrated to propose a new conceptual model of the Zhacang geothermal reservoir.

Direct sampling and analysis of fumarolic gas was conducted at Ebinokogen Ioyama volcano, Japan, between December 2015 and July 2020. Notable changes in the chemical composition of gases related to volcanic activity included a sharp increase in SO2 and H2 concentrations in May 2017 and March 2018. The analyses in March 2018 immediately preceded the April 2018 eruption at Ioyama volcano. The isotopic ratios of H2O in fumarolic gas revealed the process of formation. Up to 49% high-enthalpy magmatic vapor mixed with 51% of cold local meteoric water to generate coexisting vapor and liquid phases at 100–160 °C. Portions of the vapor and liquid phases were discharged as fumarolic gases and hot spring water, respectively. The CO2/SO2 ratio of the fumarolic gas was higher than that estimated for magmatic vapor due to SO2 hydrolysis during the formation of the vapor phase. When the flux of the magmatic vapor was high, effects of hydrolysis were small resulting in low CO2/SO2 ratios in fumarolic gases. The high apparent equilibrium temperature defined for reactions involving SO2, H2S, H2 and H2O, together with low CO2/SO2 and H2S /SO2 ratios were regarded to be precursor signals to the phreatic eruption at Ioyama volcano. The apparent equilibrium temperature increased rapidly in May 2017 and March 2018 suggesting an increased flux of magmatic vapor. Between September 2017 and January 2018, the apparent equilibrium temperature was low suggesting the suppression of magmatic vapor flux. During this period, magmatic eruptions took place at Shinmoedake volcano 5 km away from Ioyama volcano. We conclude that magma sealing and transport to Shinmoedake volcano occurred simultaneously in the magma chamber beneath Ioyama volcano.

Background Himalaya is an ecologically pristine environment. The geo-tectonic activities have shaped various environmental niches with diverse microbial populations throughout the Himalayan biosphere region. Albeit, limited information is available in terms of molecular insights into the microbiome, including the uncultured microbes, of the Himalayan habitat. Hence, a vast majority of genomic resources are still under-explored from this region. Metagenome analysis has simplified the extensive in-depth exploration of diverse habitats. In the present study, the culture-independent whole metagenome sequencing methodology was employed for microbial diversity exploration and identification of genes involved in various metabolic pathways in two geothermal springs located at different altitudes in the Sikkim Himalaya. Results The two hot springs, Polok and Reshi, have distinct abiotic conditions. The average temperature of Polok and Reshi was recorded to be 62 °C and 43 °C, respectively. Both the aquatic habitats have alkaline geochemistry with pH in the range of 7–8. Community profile analysis revealed genomic evidence of plentiful bacteria, with a minute fraction of the archaeal population in hot water reservoirs of Polok and Reshi hot spring. Mesophilic microbes belonging to Proteobacteria and Firmicutes phyla were predominant at both the sites. Polok exhibited an extravagant representation of Chloroflexi, Deinococcus-Thermus, Aquificae, and Thermotogae. Metabolic potential analysis depicted orthologous genes associated with sulfur, nitrogen, and methane metabolism, contributed by the microflora in the hydrothermal system. The genomic information of many novel carbohydrate-transforming enzymes was deciphered in the metagenomic description. Further, the genomic capacity of antimicrobial biomolecules and antibiotic resistance were discerned. Conclusion The study provided comprehensive molecular information about the microbial treasury as well as the metabolic features of the two geothermal sites. The thermal aquatic niches were found a potential bioresource of biocatalyst systems for biomass-processing. Overall, this study provides the whole metagenome based insights into the taxonomic and functional profiles of Polok and Reshi hot springs of the Sikkim Himalaya. The study generated a wealth of genomic data that can be explored for the discovery and characterization of novel genes encoding proteins of industrial importance.

The main aim of this study was to evaluate gamma radiation level in the mineral hot springs of Ardabil province in Iran. In addition, the cancer risk of gamma radiation was assessed for swimmers. Natural gamma radiation was measured using Ion Chamber Survey Meter 451B in 22 springs throughout the province. Gamma was measured at 20 cm and 100 cm above the ground level in 15 locations of each spring. Excess lifetime cancer risk was calculated to investigate the risk of exposure to gamma radiation. The highest and lowest annual absorbed dose rate of gamma were found to be 1.17(10-3) and 1.99(10-3) Sv/y at the height of 20 cm above the ground level and 5.26(10-4) and 1.52(10-3) Sv/y at the height of 100 cm above the ground level, respectively. Excess lifetime cancer risk ranged from 4.57(10-4) to 7.76(10-4) at the height of 20 cm and from 2.06(10-4) to 5.94(10-4) at the height of 100 cm which are lower than global average of 1.45(10-3) declared by the United Nations. Although the risk level in this study is lower than the global average, protective and preventive measures should be considered by individuals and authorities in these areas to reduce the effects of gamma radiation on the health of the swimmers.

Hot spring discharge was linked to the 2011 Mw 6.6 Iwaki earthquake. Periodic surveys revealed that the discharge continued for more than 7 years, which is a rare and valuable long-term record of hot spring discharge triggered by an earthquake in a non-volcanic area. In terms of coseismic changes, based on a comparison of the spatial distribution of changes in the coseismic water head and calculated crustal volumetric strain using a fault model, hot spring water discharge was found to be caused by a change in the coseismic crustal volumetric strain. As for the postseismic changes, observations over 7 years revealed a gradual rise in the temperature and chloride ion concentration of the hot spring water. Such long-term hot spring discharge may be explained by the following two causes: the rise of thermal water from the deep part and the permeability changes along the hot spring channels.

Temporal changes in volcanic water chemistry are reliable indicators of changes in volcanic activity. Conventionally, volcanic water discharges are monitored through repetitive sampling and subsequent laboratory analysis. Samples are usually taken at intervals ranging between weekly and annually due to the campaign-style of observations. However, samples collected in this way to track chemical changes were insufficient in terms of number, frequency, and temporal coverage/completeness to allow quantitative tracking of volcanic activity. In this study, we thus developed a field auto-sampling tool for collecting volcanic waters discharged near craters to improve the frequency of water sampling. The basis of the developed tool is a commercially available XY plotter, a drawing robot, which can be controlled by a computer numerical control (CNC) operator code called G-code. To collect the water in the arranged sampling bottles, the drawing pen of the XY plotter was replaced with a plastic drip pipe connected to a peristaltic pump. A field test using the G-code-Operated Field Auto-sampling Tool (GOFAT) was conducted at a hot spring at a crater area of Hakone volcano in Japan. Samples were collected at three-hour intervals for 40 consecutive days. The GOFAT successfully operated without stopping and collected a total of 332 water samples. Using the high temporal resolution samples obtained by the GOFAT, we observed short-term significant positive SO4 peaks that endured for approximately a day, which had not been detected by a repetitive sampling carried out in previous studies at this volcano. Our results clearly show the importance of high temporal resolution sampling, even during quiescent periods, to clarify the characteristics of the observed hot spring.

Genotypic and morphological diversity of cyanobacteria in the Rupite hot spring (Bulgaria) was investigated by means of optical microscopy, cultivation, single-cell PCR, and 16S rRNA gene amplicon sequencing. Altogether, 34 sites were investigated along the 71-39 °C temperature gradient. Analysis of samples from eight representative sites shown that Illumina, optical microscopy, and Roche 454 identified 72, 45 and 19% respective occurrences of all cumulatively present taxa. Optical microscopy failed to detect species of minor occurrence; whereas, amplicon sequencing technologies suffered from failed primer annealing and the presence of species with extensive extracellular polysaccharides production. Amplicon sequencing of the 16S rRNA gene V5-V6 region performed by Illumina identified the cyanobacteria most reliably to the generic level. Nevertheless, only the combined use of optical microscopy, cultivation and sequencing methods allowed for reliable estimate of the cyanobacterial diversity. Here, we show that Rupite hot-spring system hosts one of the richest cyanobacterial flora reported from a single site above 50 °C. Chlorogloeopsis sp. was the most abundant at the highest temperature (68 °C), followed by Leptolyngbya boryana, Thermoleptolyngbya albertanoae, Synechococcus bigranulatus, Oculatella sp., and Desertifilum sp. thriving above 60 °C, while Leptolyngbya geysericola, Geitlerinema splendidum, and Cyanobacterium aponinum were found above 50 °C.

This study presents hydrochemical analysis and geothermal evaluation of thermal springs located in north central Algeria for possible exploitation in agriculture, greenhouses, and residential heating. The exploitation of this energy depends on geothermal water parameters such as T°, pH, flow rate, and thermal power. Thirty one thermal springs were identified in our study area including Ouarsenis, Biban, and Kabylie provinces in the Tell Atlas, northern Algeria. These thermal springs are included by hammams, baths, and spas with hot waters exhibiting a mean temperature of 60 °C. Samples were collected during March 2018 on the thirty-one sites to evaluate the hydrochemical properties of hot waters and physicochemical parameters were measured in situ. The results show that the geothermal temperature of the reservoir in the study area is of approximately 130 °C. The temperature of hot waters varied between 22 and 80 °C. The pH revealed that the hot waters are acid; the flow rate varied from 0.8 to 30 L/s. The thermal power water calculated for all sites is ranged between 40 and 5020 KWth. This study is a part of a project related to a new global mapping of thermal spring parameters with corresponding geothermal energy potential. This potential is important for sustainable development by introducing geothermal energy instead of fossil energy.

The Isti Su hot spring is located in southeast of Salmas, in Western Azerbaijan, Iran. The area is a small part of Sanandaj–Sirjan geological zone which hosts many hot springs. The magma chamber of Salmas region is the main heat source of the hot springs in Isti Su area. Abundant rainfall and relatively long duration of snowfall as well as several deep faults in the area create the best conditions to have several hot springs in the area. The host rocks of the area are sedimentary and metamorphic rocks of Cambrian to Recent sediments which are intruded by several granite and ophiolite bodies. Several hot springs have been formed in the vicinity of these plutonic to sub-volcanic bodies. The Isti Su hot spring is one of the most typical hot springs of the Salmas region. Eight samples were collected from the study area. To investigate the seasonal changes in the field and chemical parameters and to measure trace element concentrations in dry and wet seasons, springs were sampled twice in May and November. Temperature, pH and electrical conductivity of the water samples were measured on-site. Temperatures of the selected samples range from 26.3 to 38.5 °C. The pH values of the samples vary between 6.4 and 7.5. TDS contents range from 9200 to 1790 mg/L. The results of geochemical analysis show that the As, Li, Fe, Hg, Na, and Cr are not more than WHO’s standard level. As and B are two times more than WHO’s standard level. The As and B concentrations in the hydrothermal and geothermal solutions rise higher than its standard level. World Health Organization recommended As level for drinking water is 0.01 mg/L. The Na–SO4–HCO3 triangular diagram shows that the samples are of HCO3 and Na types. Open skin scars, gangrene, malignant cancers and environmental problems are among the consequences of high concentrations of As and B. The high content of As and B in water of this hot spring can be harmful to the environment and people of the area.

A Gram-stain positive, moderately thermophilic, aerobic, spore-forming and rod-shaped bacterium, designated YIM 73012T, was isolated from a sediment sample collected from a hot spring located in Tibet, China, and was characterized by using a polyphasic taxonomy approach. The strain is oxidase positive and catalase negative. Growth occurred at 37–65 °C (optimum, 45–50 °C), at pH 6.0–8.5 (optimum, pH 7.0–7.5) and with 0.5–3.5% NaCl (optimum, 0.5–1.0%, w/v). The major fatty acids were iso-C15:0, iso-C16:0 and C16:0. The major polar lipids comprised of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylmethylethanolamine and phosphatidylglycerol. The cell wall peptidoglycan contained meso-diaminopimelic acid. The respiratory quinone was MK-7. The G+C content of genomic DNA was 43.6 mol%. Phylogenetic analyses based on 16S rRNA gene sequences showed that the strain YIM 73012T forms a distinct lineage with respect to the genus Anoxybacillus in the family Bacillaceae. Based on 16S rRNA gene sequence identities the closely related phylogenetic neighbours are Anoxybacillus caldiproteolyticus DSM 15730T (96.7%) and Saccharococcus thermophilus DSM 4749T (96.6%). Strain YIM 73012T was distinguishable from the closely related reference strains by the differences in phenotypic, chemotaxonomic and genotypic characteristics, and represents a novel species of the genus Anoxybacillus, for which the name Anoxybacillus sp. nov. is proposed. The type species is Anoxybacillus sediminis sp. nov., with the type strain YIM 73012T (= KCTC 33884T = DSM 103835T).

A geophysical investigation of a hot spring system located in Rabulu, Fiji, was carried out from October 2014 to March 2015. The investigation covered a survey area of 6075 m2. Self-potential (SP), ground temperature and soil carbon dioxide (CO2) concentrations were measured and investigated for their distribution characteristics and inter-linkages. Results indicated obvious anomalous zone at the hot spring discharge site. The SP profile analysis highlighted thermal water upwelling zones and elevation-driven subsurface groundwater pathways. Measurement of subsurface temperatures up to 1 m depths revealed increasing temperatures, indicating potentially high thermal gradients in the area. Surface soil CO2 distributions also agreed with SP and ground temperature results. The overall result of the study demonstrated that synchronised measurements of SP, ground temperature and soil CO2 can be instrumental in identifying anomalous zones near the hot spring sites. Other parameters such as spring water temperature, discharge rate and energy flux estimates from the spring were calculated and analysed. The high-dense multi-parameter data coverage allowed interpretation of geothermal features at a scale never conducted in Fiji before. The near-surface investigations reported in this study corroborate previously suggested steady geothermal activity in the region, deserving further detailed investigation.

The taxonomic positions of two moderately thermophilic bacteria, strains YIM 72259T and YIM 72238T, isolated from a hot spring sediment sample were determined using polyphasic taxonomic approaches. Pairwise comparison of the 16S rRNA gene sequences showed that strains YIM 72259T and YIM 72238T are closely related to Tepidimonas ignava SPS-1037T (97.0 and 97.5%, respectively), Tepidimonas taiwanensis I1-1T (96.5 and 97.3%), while sharing 98.0% sequence similarity with each other. The DNA–DNA relatedness values of strains YIM 72238T with T. ignava SPS-1037T and T. taiwanensis I1-1T were determined to be 25.2 ± 1.2 and 24.6 ± 3.1%, respectively, while the two strains (YIM 72259T and YIM 72238T) had a relatedness value of 38.3 ± 4.4% between themselves. The two strains were aerobic, Gram-stain negative, motile by means of a polar flagellum and formed non-pigmented colonies. The DNA G+C contents of strains YIM 72259T and YIM 72238T were determined to be 71.6 and 68.9 mol%, respectively. The major fatty acids in both strains were identified as (> 10%) C16:0, C17:0 and summed feature 8, while the strain YIM 72238T contained a moderately high amount of summed feature 3 as well. The polar lipid profiles for strains YIM 72259T and YIM 72238T consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, an unidentified aminolipid and several unidentified phospholipids. Besides the morphological and chemotaxonomic characteristics, phylogenetic analyses of the 16S rRNA gene sequences and the biochemical characteristics indicated that the two strains represented two novel members of the genus Tepidimonas, for which the name Tepidimonas sediminis sp. nov. [type strain YIM 72259T (= NBRC 112410T = CGMCC 1.15971T) and Tepidimonas alkaliphilus sp. nov. [type strain YIM 72238T (= KCTC 52717T = CCTCC AB 2017168T)] are proposed.

Natural springs have the potential to provide important information on hydrogeochemical processes within aquifers. This study used traditional and classic technical methods and procedures to determine the characteristics and evolution of springs to gain further knowledge on the differences between hot saline springs and cold fresh springs. In a short river segment near Wenquanzhen in the eastern Sichuan Basin, southwest China, several natural springs coexist with total dissolved solids (TDS) ranging from less than 1 to 15 g/L and temperatures from 15 to 40 °C. The springs emanate from the outcropping Lower and Middle Triassic carbonates in the river valley cutting the core of an anticline. The cold springs are of Cl·HCO3-Na·Ca and Cl·SO4-Na types, and the hot saline springs are mainly of Cl-Na type. The chemistry of the springs has undergone some changes with time. The stable hydrogen and oxygen isotopes indicate that the spring waters are of a meteoric origin. The salinity of the springs originates from dissolution of minerals, including halite, gypsum, calcite and dolomite. The evolution of the springs involves the following mechanisms: the groundwater receives recharge from infiltration of precipitation, then undergoes deep circulation in the core of the anticline (incongruent dissolution of the salt-bearing strata occurs), and emerges in the river valley in the form of hot springs with high TDS. Groundwater also undergoes shallow circulation in the northern and southern flanks of the anticline and appears in the river valley in the form of cold springs with low TDS.

Death Valley located in the Zagros Mountains, Khuzestan Province, Iran, along the Bangeston Fault line is a unique landscape. Water flows from a hot headstream through a colorful bed into the valley for about 2 km down-run and disappears through the alluvial deposits. This spring and its surrounding area were found to be deadly for both animals and humans. In the last decade, it has been reported that five persons and many animals have died. The reason for the toxicity of this water has not yet been specified. Attempts have been made to find out the secret behind death. The purpose of this paper is to study the Death Valley, which is located in the south of Iran (Tashan), as well as the lethal agent and other index mineral compounds in its water. Air analysis was performed near the headstream to find more about the fatal gas in the area. The results showed that the concentration of hydrogen sulfide was as high as 400 ppm near the spring during hot season, which could lead to pulmonary edema and death. Water in the area contains a high concentration of sulfide (1780 mg/L), which is a characteristic of thermal or hot spring waters. This gas is available along the stream and also far from the spring. The amount of spring water is high enough to be exploited for remedial purposes.

Anoxybacillus flavithermus AK1 is a thermophilic bacterium that is able to survive at temperatures ranging from 55 to 60 $${^{\circ}}\hbox {C}$$ . The AK1 strain was isolated from the hot spring “Al-Ain Alhara” located at a distance of 50 km southeast of the city of Gazan, Saudi Arabia. This study presents the morphological characterization of A. flavithermus AK1, including a detailed description of its complete genome sequence. A total of 50 contigs were used to produce a genome sequence of 2,630,664 bp that includes 2724 protein-coding genes and 75 RNA genes, 18 of which are rRNA genes. A comparison of this genome sequence with those of Anoxybacillus flavithermus strains that were previously submitted to NCBI revealed that the AK1 strain has the smallest genome size with the highest GC content. The strain can therefore be exploited for several biotechnological applications based on its high thermophilic potential.

In this study, 26 Cyanophyta and Chlorophyta microalgae were isolated from high-background radiation areas in Iran. Among them, one green alga showed the highest radionuclide sorption capacity. This uranium- and radium-resistant microalga belongs to the genus Graesiella, and based on its morphological and molecular characteristics, it was identified as Graesiella emersonii Shihira and R.W. Krauss. The sample was isolated from the Ab-e-Siah hot spring in Ramsar (a city in northern Iran) with a 226Ra content of 130 Bq L−1. This strain exhibited maximum sorption capacities of 69 kBq g−1 of 226Ra and 530 mg g−1 of 238U. The optimum conditions for removal of the radionuclides were determined, and the results showed that the pH and initial cell concentration significantly affected radionuclide sorption. Furthermore, the experimental data were well-fitted to the Langmuir isotherm and pseudo-second-order kinetic models. FT-IR spectra and SEM analyses showed the mechanisms of the sorption process. The results of the present study indicated that the green alga G. emersonii, can serve as an appropriate candidate for designing an efficient sorption system for an area contaminated by 226Ra and 238U radionuclides.

Two Gram-negative, moderately thermophilic, yellow-pigmented, rod-shaped and motile bacterial strains, designated YIM 75003T and YIM 75004T, were isolated from sediment samples collected from the Tagejia hot spring in Tibet, western China. The taxonomic affiliation of the two strains was investigated by a polyphasic approach. Pairwise comparison of the 16S rRNA gene sequences showed that strains YIM 75003T and YIM 75004T are closely related to Altererythrobacter buctense M0322T (97.2 and 97.1% respectively), while sharing 99.9% sequence similarity against each other. Optimum growth of the two strains was observed at 37–45 °C, pH 8.0 and in the presence of 1–6% NaCl (w/v). Their predominant respiratory quinone was found to be ubiquinone 10. The major fatty acids in both the strains were identified as summed feature 8 (C18:1 ω6c and/or C18:1 ω7c) and summed feature 4 (C17:1 anteiso B and/or iso I). Their major polar lipid profiles were found to be diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol and sphingoglycolipid. The DNA G+C contents of strains YIM 75003T and YIM 75004T were determined to be 61.3 and 60.1 mol%, respectively. The DNA-DNA hybridization values between strains YIM 75003T and YIM 75004T, and between the two strains and their closely related phylogenetic neighbour A. buctense M0322T (=CGMCC 1.12871T) were less than 70%. Based on the morphological and physiological properties, phylogenetic analyses, chemotaxonomic characteristics and DNA–DNA relatedness values, the two strains can be distinguished from each other and from their phylogenetically closely related strain. Strains YIM 75003T and YIM 75004T are, therefore, considered to represent two novel species of the genus Altererythrobacter, for which the names Altererythrobacter lauratis sp. nov. (type strain YIM 75003T = KCTC 52606T = CCTCC AB2016268T) and Altererythrobacter palmitatis sp. nov. (type strain YIM 75004T = KCTC 52607T = CCTCC AB2016270T) are proposed.

Diatoms have been recognized as a promising raw material for biodiesel production as a result of their thermal stability. However, potent thermotolerant strains of diatoms, such as hot spring diatoms, have not yet been studied. Achnanthidium exiguum AARL D025–2 was originally isolated from a habitat at temperatures ranging from 39 to 45 °C; however, it could only be isolated and maintained at 30 °C. Hence, it has been determined that certain factors have a considerable impact on the thermostability of this diatom. One factor that has not yet been given as much consideration is pH. The pH can be significant for the growing conditions and physiology of algal cells. Thus, this study aims to investigate the effect of pH on thermotolerant diatom cultivation. The diatom A. exiguum AARL D025–2 was cultivated in modified Bold Basal Medium at different pH (7.0, 8.0, 9.0, and 10.0) and at temperatures of 30, 40, and 50 °C. Growth was monitored by direct cell-counting, while fatty acid methyl ester (FAME) composition was also examined. The results showed that an alkaline pH could promote the heat tolerance of this diatom. The optimal culture conditions for biomass and FAME production was pH 9 at 40 °C. The major FAMEs were C16-C18, which may be suitable for the purposes of biodiesel production. The results from this research study will be useful for the future development of thermotolerant diatom cultivation with regard to the study and promotion of alternative energy sources.

A natural thermal habitat, Tulasi Shyam, was studied for the culture-dependent and culture-independent diversity of the thermophilic bacteria. Soil and water samples of winter, summer and monsoon seasons were analyzed to assess the impact of the seasonal variation on the microbial diversity. The soil was fertile and contained high humic substances. The temperature of the water was 50 °C, which did not significantly vary with seasons. Various methods were assessed for the extraction of the metagenomic DNA to obtain quality DNA in good quantity. The 16S rRNA genes were amplified using the metagenomic DNA as template and the products were analyzed further by the denaturing gradient gel electrophoresis (DGGE) for evaluating the bacterial diversity. The metagenomic diversity of the hot spring reservoir-1 as compared to reservoir-2 was less influenced by the seasonal variations. The DGGE patterns of the soil samples suggested significant effect of the seasonal changes. The metagenomic diversity was distinct when compared with the culture-dependent microbial diversity. The diversity was further analyzed by the principal component analysis (PCA) and diversity indices. The apparent shift in the diversity appears to be governed by the prevailing environmental conditions.

Recurrent groundwater radon anomalous declines were observed from well measurements in the Antung hot spring area (eastern Taiwan) prior to five of six earthquakes that occurred between 2003 and 2011 (M w range 5.0–6.8). The relationship between the detectability of radon anomalies and the first motions of P-waves was investigated. Based on the first motions of P-waves recorded near the investigated well, a precursory decrease in groundwater radon can be detected only when the first motion is compression. No precursory change in groundwater radon concentration was observed for the downward first motion of P-waves.

The Hakata hot springs area is located in Fukuoka City, which is in the southwestern part of Japan. Gamma-ray and gravity surveys were conducted to understand the relationship between the low-temperature hydrothermal systems and geophysical data of the area. The depth of the reservoir basement, which was derived from gravity data, gradually deepens toward the east; it includes some steep depth gradients in the Hakata hot springs area. High intensities of gamma-rays were detected around these gradients. In addition, higher hot spring temperatures and flow rates can be observed in this area. These results indicate that some part of the level of the basement where the hot springs are concentrated is a part of the Kego Fault and is similar to the fracture zone created by past activities of the fault. Moreover, these steep depth gradients act as a path for hot spring water from the deeper side of the granitic body to the surface.

The 2016 Kumamoto earthquake (Mw 7.0) caused hot springs in the Uchinomaki area of Aso caldera to become dormant. Geodetic and borehole observations have previously demonstrated that the area around the hot springs slid horizontally ~ 2 m to the northwest during the earthquake. However, the subsurface structure in the area has not been investigated and the mechanism of sliding is unclear. To reveal geological structures in and around the hot spring area, we conducted a seismic microtremor survey at 60 sites and used the Extended Spatial Auto Correlation (ESPAC) method to determine surface-wave dispersion curves from the microtremor data. We then derived S-wave velocity profiles by inversion of the dispersion curves and constructed from them a 3D S-wave velocity model to ~ 100 m depth over the hot springs and surrounding areas. New surface fissures (indicative of extension) that opened during the 2016 earthquake correspond to a boundary in the southeast of the study area between modeled lower velocities (to the northwest) and higher velocities (to the southeast). In the central area of the hot springs, where the largest displacement occurred, the 3D model shows a plume-like high-velocity anomaly, indicative of more-competent sediments there. The lowest S-wave velocities (less-competent rocks) are in paddy fields north of the hot spring area. We interpret the above aspects of the 3D velocity model to indicate that during the 2016 earthquake the relatively competent (higher S-wave velocity) sediments in the central area of the hot springs slid northwestward, causing compressional deformation of the less-competent (lower S-wave velocity) sediments in the northern paddy fields and extensional deformation (fissures) southeast of the sliding block. A distinct increase in S-wave velocity at ~ 50 m depth coincides with the depth of a pumice layer in drillcore from the central hot spring area. Shaking during the 2016 earthquake could have caused a sudden increase in pore pressure in this widely distributed porous layer, thus providing a slip plane for the observed horizontal sliding to the northwest.

This study reports the chemical and isotopic compositions of hot-spring waters and fumarolic gases sampled in the Jigokudani Valley of Tateyama Volcano (central Japan) in 2015 and 2016 to reveal the state of the underlying hydrothermal system. We discuss the cause of temporal variations in geochemical data in terms of temperature change in the hydrothermal system and clarify the relationship between hot-spring waters and fumarolic gases. The volcanic gas supplied from deep-seated magma was separated into liquid and vapor phases when it reached a shallow depth. Each phase formed the following three types of hot-spring water: (1) high anion concentrations and isotopic compositions similar to magmatic water, (2) lower isotopic compositions compared to type-1 waters and large variations in Cl−/SO42−, and (3) low Cl− and total anion concentrations. The formation of type-1 and type-2 hot springs was influenced by magmatic components such as HCl and SO2. We consider that type-1 hot springs are derived from the liquid phase while type-2 hot springs are derived from the vapor phase of the two-phase zone. The temporal variations in Cl−/SO42− are considered to result from temperature changes in the reservoir where liquid and vapor separated, as the HCl partitioning coefficient between the vapor and liquid phases is strongly dependent on temperature. Type-3 hot springs are derived from the vapor phase, which is depleted in HCl and SO2. We propose that the Cl− concentration of type-2 hot springs could be a measure of volcanic activity because it reflects the thermal state of the shallow two-phase zone where phreatic eruptions occur.

Background Hot spring bacteria have unique biological adaptations to survive the extreme conditions of these environments; these bacteria produce thermostable enzymes that can be used in biotechnological and industrial applications. However, sequencing these bacteria is complex, since it is not possible to culture them. As an alternative, genome shotgun sequencing of whole microbial communities can be used. The problem is that the classification of sequences within a metagenomic dataset is very challenging particularly when they include unknown microorganisms since they lack genomic reference. We failed to recover a bacterium genome from a hot spring metagenome using the available software tools, so we develop a new tool that allowed us to recover most of this genome. Results We present a proteobacteria draft genome reconstructed from a Colombian’s Andes hot spring metagenome. The genome seems to be from a new lineage within the family Rhodanobacteraceae of the class Gammaproteobacteria, closely related to the genus Dokdonella. We were able to generate this genome thanks to CLAME. CLAME, from Spanish “CLAsificador MEtagenomico”, is a tool to group reads in bins. We show that most reads from each bin belong to a single chromosome. CLAME is very effective recovering most of the reads belonging to the predominant species within a metagenome. Conclusions We developed a tool that can be used to extract genomes (or parts of them) from a complex metagenome. Electronic supplementary material The online version of this article (10.1186/s12864-018-5191-y) contains supplementary material, which is available to authorized users.

Previous studies on the redox potential of hot springs have indicated that redox potential sensors display a more heightened sensitivity to the HS−/SO4 2− redox couple, and that redox potential is not related to many different redox couples. However, previous studies have not focused on long-term, continuous measurement of hot spring aquifers. Therefore, three continuous in situ redox potential (Eh) measurements, each lasting approximately 1 month, were conducted using a platinum electrode in a 32 °C hot spring aquifer. Measured Eh values were −353, −343, and −329 mV in the three monitoring campaigns. The chemical properties of water sampled from the aquifer indicate that S2− concentrations ranged from 0.04 to 0.19 mg/L and Fe concentrations were below the quantification limit (

Finding productive boreholes in the Karoo fractured aquifers has never been an easy task. Fractured Karoo aquifers in the neotectonic zones in the Eastern Cape Province can be targeted for groundwater exploration. The Polile Tshisa hot spring is located in a seismo-tectonic region beset by neotectonics. Hot springs are indicative of circulation of groundwater at great depths along fault zones, and accordingly of neotectonics. The characterisation of hot springs by means of magnetic and electromagnetic methods can help infer the occurrence of structures which are favourable for groundwater potential. The Polile Tshisa hot spring is characterised by faults, fractures, and dolerite dykes. All these structures make the hot spring a good case study for groundwater exploration.

Eight thermophilic bacterial strains were isolated from Tattapani Hot spring and screened for various hydrolytic enzymes including cellulases. The isolated bacterial strains were identified as Geobacillus thermodenitrificans IP_WH1(KP842609), Bacillus licheniformis IP_WH2(KP842610), B. aerius IP_WH3(KP842611), B. licheniformis IP_WH4(KP842612), B. licheniformis IP_60Y(KP842613), G. thermodenitrificans IP_60A1(KP842614), Geobacillus sp. IP_60A2(KP842615) and Geobacillus sp. IP_80TP(KP842616) after 16S ribotying. Out of the eight isolates Geobacillus sp. IP_80TP grew best at 80 °C whereas rest of the isolates showed optimal growth at 60 °C. G. thermodenitrificans IP_WH1 produced a thermotolerant cellulase with maximum activity at 60 °C.

© 2016 International Society for Microbial Ecology All rights reserved. Although little is known regarding microbial life within our planet's rock-hosted deep subseafloor biosphere, boreholes drilled through deep ocean sediment and into the underlying basaltic crust provide invaluable windows of access that have been used previously to document the presence of microorganisms within fluids percolating through the deep ocean crust. In this study, the analysis of 1.7 million small subunit ribosomal RNA genes amplified and sequenced from marine sediment, bottom seawater and basalt-hosted deep subseafloor fluids that span multiple years and locations on the Juan de Fuca Ridge flank was used to quantitatively delineate a subseafloor microbiome comprised of distinct bacteria and archaea. Hot, anoxic crustal fluids tapped by newly installed seafloor sampling observatories at boreholes U1362A and U1362B contained abundant bacterial lineages of phylogenetically unique Nitrospirae, Aminicenantes, Calescamantes and Chloroflexi. Although less abundant, the domain Archaea was dominated by unique, uncultivated lineages of marine benthic group E, the Terrestrial Hot Spring Crenarchaeotic Group, the Bathyarchaeota and relatives of cultivated, sulfate-reducing Archaeoglobi. Consistent with recent geochemical measurements and bioenergetic predictions, the potential importance of methane cycling and sulfate reduction were imprinted within the basalt-hosted deep subseafloor crustal fluid microbial community. This unique window of access to the deep ocean subsurface basement reveals a microbial landscape that exhibits previously undetected spatial heterogeneity.

A systematic optimization process for simple and eco-friendly extracellular biosynthesis of gold nanoparticles by a native thermophilic Ureibacillus thermosphaericus strain thermo-BF isolated from geothermal hot springs has been presented. Biosynthesis reactions were conducted using the culture supernatant at different temperatures (60–80 °C) and pH (6–9) with gold ion concentration ranging from 0.001 to 0.1 M. The results obtained showed that pure spherical nanoparticles in the range of 35–75 nm were produced, and the maximum nanoparticle production was achieved using 0.001 M HAuCl4 at 80 °C, pH 9. Genome mining and profiling of the genes encoding bioreducing enzymes in U. hermosphaericus strain thermo-BF revealed evidences indicating sulfur reduction capability of this bacterium. Overall, the findings of this study confirmed the great biocatalyzing potential of the extermophilic U. thermosphaericus strain thermo-BF supernatant for intensified biosynthesis of gold nanoparticle under extreme conditions.

The behavior of mercury (Hg) in water, sediments, air, dwarf bamboo leaves, and soils around the fumarolic area of Mt. Myoko, Japan, was investigated. Although some of the hot spring water samples contained over 1 µg/L total-Hg, overall, the total-Hg concentrations in the water samples decreased rapidly as the water flowed into a river. The total-Hg concentrations decreased not only due to simple dilution, but also to co-precipitation of Hg2+ with Fe(OH)3. The highest atmospheric Hg concentration, 91.7 ng/m3, was detected near the fumarole, and the concentrations decreased with distance from the fumarolic area. This tendency was also confirmed in the total-Hg concentrations of plant leaf samples. Total-Hg, methylmercury (MeHg), and ethylmercury (EtHg) concentrations in the soil surface layer (n = 13) ranged from 0.19 to 21.7 mg/kg, 0.3 to 9.3 µg/kg, and undetected to 7.7 µg/kg, respectively. The total-Hg concentrations in the surface layer soil samples decreased with distance from the fumarolic area, while the vertical distribution of total-Hg concentrations in the core and outcrop samples showed no clear trends. However, the MeHg and EtHg concentrations had no relationship with the total-Hg concentrations and were higher in the upper layer soils. The results suggest that MeHg and EtHg not only migrate with other Hg species from the volcanic gases, but are also generated on site. It was also confirmed that EtHg occurs in soil at the same level as MeHg in the study area.

Geothermal power seems to be a potential source of green energy in India. But these renewable energy resources are still ignored in India even after having a lot of potential sources as seen in more than 300 hot springs scattered throughout different geothermal areas of the country. Many of them could be utilized for power generation using the earth’s internal heat. More hours are needed to explore these geothermal areas using geochemical, geophysical techniques, and statistical analysis to qualitatively estimate power harnessing capabilities and sustainability of the areas for generation of geothermal power. In the present paper, attention has been focused to investigate Bakreswar geothermal field of India by continuous (24*7) and online monitoring of terrestrial gases such as He and radioactive gases (222Rn) in hot spring emanations of the geothermal area for more than 5 years along with discrete measurement of some other geochemical and geophysical parameters. The discrete measures imply that the seven hot spring vents at the study area are linked to the aquifer through different ways covering non-uniform rock assemblies and ascertain the presence of high amount of radioactive minerals at the underneath terrains. Stable activities with a high-out flux of 222Rn and He for a prolonged time period is expected within the reservoir present at the study area as consequence of analysis of the temporal variations and statistical measures of the continuous data sets. Seasonal variation of time series data also recommends that the high amount of radioactive sources present at the crust of the reservoir is able to produce enough quantity of heat irrespective of meteorological effects. The investigation on the power spectra interferes that the geothermal system is still in quite active phase on the influence of tectonic activities. Therefore, the geothermal reservoir present at the Bakreswar geothermal area may be utilized as a constant and continuous heat source for a long time period to run a geothermal power plant.